Supplemental restraint systems or airbags have become an important safety feature in today's automobiles. Airbag deployment technology currently uses a controlled combustion or an explosion to rapidly deploy the airbag. The chemicals that create this controlled explosion are housed in a combustion chamber or housing. The combustion gas products are expelled from the chamber through a diffuser into the airbag to deploy or inflate the airbag.
A number of techniques are known to inflate the airbag, such as the use, through combustion, of powdered sodium azide. The combustion reaction creates an instantaneous increase in pressure of between about 12,000 pounds per square inch (psi) and about 16,000 psi. This instantaneous pressure increase inflates the airbag.
Airbag deployment requires proper diffusion of the combustion gases to inflate the airbag. One known deployment system includes a combustion chamber, for carrying out and containing the combustion process. The chamber includes an opening in an end thereof for directing the combustion gases. The combustion chamber is mounted or connected to a diffuser, at the opening in the chamber, that is in flow communication with the interior region of the airbag.
The diffuser extends into the airbag and diffuses or distributes the gases generated from the combustion process within the airbag to properly deploy the bag. The diffuser must have sufficient open or flow area to permit the gases to flow from the combustion chamber into the airbag to rapidly and properly deploy the bag.
A burst disk is positioned at about the combustion chamber opening. The burst disk isolates the diffuser from the combustion chamber prior to combustion, and prevents the combustion products from rupturing the wall of the combustion chamber or flowing backward out through the chamber upon deployment.
Because of the explosive nature of the combustion process, it has been observed that debris, such as burst disk portions or fragments and combustion product powder particles can be generated. This debris is not intended to enter the airbag upon deployment. Rather, the debris is isolated and remains within the combustion chamber and diffuser subsequent to combustion.
One arrangement that is used to retain this debris within the combustion chamber and diffuser includes a generally cylindrical diffuser having a plurality, e.g., eight, large apertures therein and a steel screen positioned within the diffuser. The screen includes a large number of relatively small openings to prevent egress of the debris subsequent to combustion. The diffuser includes a separate end wall that is secured, such as by welding, to the diffuser at the connection to the combustion chamber after the screen is mounted in the diffuser.
Although this arrangement works well for its intended function, there are multiple parts and manufacturing process steps required to fabricate the diffuser and to fixedly position the screen within the diffuser. As such, this part can be relatively costly to manufacture.
Attempts have been made to utilize other configurations that provide sufficient flow area to assure rapid deployment of the airbag, while at the same time maintaining debris within the combustion chamber and diffuser. Such configurations include the drilling or punching a plurality of small openings within the diffusion chamber wall. Such manufacturing processes are, however, costly and can require frequent maintenance of the machining or manufacturing parts.
In addition, it has been found that drilling or punching the openings in the diffuser cannot be performed with reliability after the diffuser is fully formed. That is, when the bottom end wall of the diffuser is formed after the openings are drilled or punched, the openings tend to become deformed as a result of the wall formation. Deformation of the openings can result in less than optimal diffusion characteristics for the diffuser. On the other hand, when attempting to punch or drill the openings after the bottom wall is formed, the machining operation can become maintenance intensive. As a result, known diffusers utilize a multiple-piece construction.
Accordingly, there continues to be a need for a diffuser that is readily manufactured, and that incorporates debris retaining characteristics while at the same time providing sufficient flow area for rapid deployment of the airbag. Such as diffuser is a one-piece member that is cost-effective to manufacture and does not adversely effect or increase machine-tool maintenance.